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  <div class="section" id="using-the-c-api-when-embedding">
<h1>Using the C API when Embedding<a class="headerlink" href="#using-the-c-api-when-embedding" title="Permalink to this headline">¶</a></h1>
<p>The <a class="reference internal" href="c_api.html#ref-c-api"><span>C API</span></a> is intended to be called from handwritten code in
SIP generated modules.  However it is also often necessary to call it from C or
C++ applications that embed the Python interpreter and need to pass C or C++
instances between the application and the interpreter.</p>
<p>The API is exported by the SIP module as a <code class="docutils literal"><span class="pre">sipAPIDef</span></code> data structure
containing a set of function pointers.  The data structure is defined in the
SIP header file <code class="docutils literal"><span class="pre">sip.h</span></code>.  When using Python v2.7, or Python v3.1 or later the
data structure is wrapped as a Python <code class="docutils literal"><span class="pre">PyCapsule</span></code> object.  When using other
versions of Python the data structure is wrapped as a Python <code class="docutils literal"><span class="pre">PyCObject</span></code>
object.  It is referenced by the name <code class="docutils literal"><span class="pre">_C_API</span></code> in the SIP module dictionary.</p>
<p>Each member of the data structure is a pointer to one of the functions of the
SIP API.  The name of the member can be derived from the function name by
replacing the <code class="docutils literal"><span class="pre">sip</span></code> prefix with <code class="docutils literal"><span class="pre">api</span></code> and converting each word in the
name to lower case and preceding it with an underscore.  For example:</p>
<blockquote>
<div><p><code class="docutils literal"><span class="pre">sipExportSymbol</span></code> becomes <code class="docutils literal"><span class="pre">api_export_symbol</span></code></p>
<p><code class="docutils literal"><span class="pre">sipWrapperCheck</span></code> becomes <code class="docutils literal"><span class="pre">api_wrapper_check</span></code></p>
</div></blockquote>
<p>Note that the type objects that SIP generates for a wrapped module (see
<a class="reference internal" href="c_api.html#ref-type-structures"><span>Generated Type Structures</span></a>, <a class="reference internal" href="c_api.html#ref-enum-type-objects"><span>Generated Named Enum Type Objects</span></a> and
<a class="reference internal" href="c_api.html#ref-exception-objects"><span>Generated Exception Objects</span></a>) cannot be refered to directly and must be
obtained using the <a class="reference internal" href="c_api.html#c.sipFindType" title="sipFindType"><code class="xref c c-func docutils literal"><span class="pre">sipFindType()</span></code></a> function.  Of course, the
corresponding modules must already have been imported into the interpreter.</p>
<p>The following code fragment shows how to get a pointer to the <code class="docutils literal"><span class="pre">sipAPIDef</span></code>
data structure:</p>
<div class="highlight-python"><div class="highlight"><pre>#include &lt;sip.h&gt;

const sipAPIDef *get_sip_api()
{
#if defined(SIP_USE_PYCAPSULE)
    return (const sipAPIDef *)PyCapsule_Import(&quot;sip._C_API&quot;, 0);
#else
    PyObject *sip_module;
    PyObject *sip_module_dict;
    PyObject *c_api;

    /* Import the SIP module. */
    sip_module = PyImport_ImportModule(&quot;sip&quot;);

    if (sip_module == NULL)
        return NULL;

    /* Get the module&#39;s dictionary. */
    sip_module_dict = PyModule_GetDict(sip_module);

    /* Get the &quot;_C_API&quot; attribute. */
    c_api = PyDict_GetItemString(sip_module_dict, &quot;_C_API&quot;);

    if (c_api == NULL)
        return NULL;

    /* Sanity check that it is the right type. */
    if (!PyCObject_Check(c_api))
        return NULL;

    /* Get the actual pointer from the object. */
    return (const sipAPIDef *)PyCObject_AsVoidPtr(c_api);
#endif
}
</pre></div>
</div>
<p>The use of <a class="reference internal" href="c_api.html#c.SIP_USE_PYCAPSULE" title="SIP_USE_PYCAPSULE"><code class="xref c c-macro docutils literal"><span class="pre">SIP_USE_PYCAPSULE</span></code></a> means that code will run under all
versions of Python.</p>
</div>


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